Conversion form Decibels to voltage and ratio

The table shows the ratio and voltage equivlent to a given level in dBu from +40 dBu to -40 dBu

dBu is a logrithmic voltage notation relative to 0.7746 Volts but not related to any impedance.
dBm (the traditional unit 50 years ago) is relative to 1 mW into 600 ohms and is numerically equal to dBu.

dBV (rarely used) is relative to 1.0 Volts and like dBu, is not related to any impedance.